Accessing attributes of an MO that overlap with python reserved words fails

[mtimm]

Example:

>>> from cobra.mit.access import MoDirectory
>>> from cobra.mit.session import LoginSession
>>> ls = LoginSession('http://10.1.1.200', 'admin', 'p@ssw0rd)
>>> md = MoDirectory(ls)
>>> md.login()
>>> encap = md.lookupByClass("fvnsEncapBlk")
>>> encap[0].to
'vlan-2230'
>>> encap[0].from
  File "<stdin>", line 1
    encap[0].from
                ^
SyntaxError: invalid syntax
>>> encap[0].from_
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "cobra/mit/mo.py", line 100, in __getattr__
    return BaseMo.__getattr__(self, propName)
  File "cobra/internal/base/moimpl.py", line 288, in __getattr__
    return self.__children._getChildContainer(attrName)
  File "cobra/internal/base/moimpl.py", line 193, in _getChildContainer
    childPrefix)
AttributeError: No class with prefix "from_" found
>>> getattr(encap[0], "from")
'vlan-2220'
>>> 

We need a generic solution to access an attribute that overlaps with a python builtin/reserved keyword or to document how to access attributes like this in a more clear way.

PropMeta shows the original attribute and not the one with an _ appended to it:

>>> pprint(vars(encap[0].meta.props))
{'_props': {'allocMode': <cobra.mit.meta.PropMeta object at 0x1079383d0>,
            'childAction': <cobra.mit.meta.PropMeta object at 0x1079384d0>,
            'descr': <cobra.mit.meta.PropMeta object at 0x1079385d0>,
            'dn': <cobra.mit.meta.PropMeta object at 0x107938610>,
            'from': <cobra.mit.meta.PropMeta object at 0x107938650>,
            'lcOwn': <cobra.mit.meta.PropMeta object at 0x107938690>,
            'modTs': <cobra.mit.meta.PropMeta object at 0x107938810>,
            'name': <cobra.mit.meta.PropMeta object at 0x107938890>,
            'rn': <cobra.mit.meta.PropMeta object at 0x1079388d0>,
            'status': <cobra.mit.meta.PropMeta object at 0x107938910>,
            'to': <cobra.mit.meta.PropMeta object at 0x107938a10>,
            'uid': <cobra.mit.meta.PropMeta object at 0x107938a50>}}
>>> 

[JLeClerc]

getattr() will work:

from cobra.mit.access import MoDirectory
from cobra.mit.session import LoginSession
ls = LoginSession('http://10.1.1.200', 'admin', 'p@ssw0rd)
md = MoDirectory(ls)
md.login()
encap = md.lookupByClass("fvnsEncapBlk")
encap[0].from
#>>> *** SyntaxError: invalid syntax (<stdin>, line 1)

getattr(encap[0], 'from')
#>>> 'vlan-1500'

[mtimm]

Hi Joe,

I included the getattr workaround in my original description of the problem.

Mike

[JLeClerc]

Hi Mike,

Sorry, I read that too quickly the first time. Restating the problem, we cannot access object attributes through dot-notation because they conflict with Python reserved keywords which causes the parser to raise a syntax error. So we either have to change the attribute names or use something other than dot notation.

Solution #1 - obvious and likely a bad idea - change the attribute names:

@property
def From(self):
    return self._from

Solution #2 - using something other than dot-notation (or getattr() function directly) - e.g ElementTree-style access

# getattr
encap[0].attrib['from']
# setattr
encap[0].update({'desc': 'outside encap'})

I could write something similar to #2 - we just need to decide what the syntax should look like.

Thanks,
Joe

[mtimm]

When we generate the model for cobra we explicitly change the attribute names that overlap with python reserved words to include an _ at the end, in this case the model should have from_. However, it doesn't appear that we carry this forward inside cobra so when we instantiate the property we do so with the original name which is in propMeta, I haven't looked into why this is though.